Configuring Layer 2 Etherchannels - Cisco WS-C3750-48PS-S Software Configuration Manual

Configuring EtherChannels
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Configuring Layer 2 EtherChannels

You configure Layer 2 EtherChannels by assigning ports to a channel group with the channel-group
interface configuration command. This command automatically creates the port-channel logical
interface.
If you enabled PAgP on a port in the auto or desirable mode, you must reconfigure it for the on mode
by using the channel-group channel-group-number mode on interface configuration command before
adding this port to a cross-stack EtherChannel. PAgP is not supported on cross-stack EtherChannels.
If you enabled LACP on a port in the active or passive mode, you must reconfigure it for the on mode
by using the channel-group channel-group-number mode on interface configuration command before
adding this port to a cross-stack EtherChannel. LACP is not supported on cross-stack EtherChannels.
Catalyst 3750 Switch Software Configuration Guide
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For Layer 2 EtherChannels:
Assign all ports in the EtherChannel to the same VLAN, or configure them as trunks. Ports with
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different native VLANs cannot form an EtherChannel.
– If you configure an EtherChannel from trunk ports, verify that the trunking mode (ISL or
802.1Q) is the same on all the trunks. Inconsistent trunk modes on EtherChannel ports can have
unexpected results.
An EtherChannel supports the same allowed range of VLANs on all the ports in a trunking
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Layer 2 EtherChannel. If the allowed range of VLANs is not the same, the ports do not form an
EtherChannel even when PAgP is set to the auto or desirable mode.
Ports with different spanning-tree path costs can form an EtherChannel if they are otherwise
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compatibly configured. Setting different spanning-tree path costs does not, by itself, make ports
incompatible for the formation of an EtherChannel.
For Layer 3 EtherChannels, assign the Layer 3 address to the port-channel logical interface, not to
the physical ports in the channel.
For cross-stack EtherChannel configurations, disable PAgP and LACP on all ports targeted for the
EtherChannel by using the channel-group channel-group-number mode on interface configuration
command. Before adding a stack member port to an existing EtherChannel, manually disable PAgP
and LACP on all the ports that are members of the channel group, and then manually configure the
cross-stack EtherChannel. PAgP and LACP are not supported on cross-stack EtherChannels.
If cross-stack EtherChannel is configured and the switch stack partitions, loops and forwarding
misbehaviors can occur.
Chapter 33 Configuring EtherChannels
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